After several years of playing a 21” scale 17-fret, open back tenor banjo pain-free, the switch to the 23” scale was enough of a difference in arm position to cause a pain in my (right) shoulder. I almost immediately experienced shoulder pain upon playing this new banjo. I’m left handed so my right shoulder is the right-handed person’s left shoulder. Basically, it’s the shoulder on the fretting arm, not the picking arm. The additional weight of the resonator banjo probably didn't help.
A 19-fret tenor banjo is still a shorter scale than a typical 5-string banjo, so it's probably not as bad as it could be. I did a little bit of research and saw some suggestions to use a strap to support the neck and to also try positioning the neck at a lower angle, more parallel with the floor. (I like to hold it fairly upright at about a 45 degree angle).
This has definitely caused me to be mindful of any potential for inflammation and has also made me more conscious of how I hold my body and the banjo, and even how I reach out to the tuning pegs. Lowering the neck still feels awkward and sometimes I unknowingly revert back to having it pointed more toward the ceiling.
The soreness is not there every time I play, but sometimes it does come back. I am hoping that it goes away altogether with time as my body adjusts. It is strange that such a small change from a 21” scale neck to a 23” scale neck has caused this flare up in the shoulder. The fingers on my fretting hand have been able to adapt to the longer stretch without many issues.